1. Technical Field
The invention relates to a powertrain for a hybrid electric vehicle with front traction wheels.
2. Background of the Invention
A known hybrid electric vehicle powertrain system with two operating modes includes two motor-generators and two planetary gear units, which are adaptable particularly for rearwheel drive vehicle applications. One of the two motor-generators is situated between the two planetary gear units and the second motor-generator is located remotely from the engine at the torque output side of the second motor-generator. The two gear units establish either a split power input drive mode or a compound split power drive mode depending upon vehicle speed and other powertrain variables. Provision is made using selectively engageable clutches for shifting between the two drive modes at a zero speed point for one of the motor-generators. The clutches can be engaged and released in a synchronous fashion to establish an input split drive mode with a reverse drive and a forward drive range. When operating in this mode, one of the motor-generators acts as a motor and the other acts as a generator.
When a compound torque split mode is established, the powertrain may act in a high forward drive range. At that time, the motor-generators can operate in either a motoring mode or a generating mode as the vehicle speed changes.
The known two-mode hybrid electric vehicle powertrain is suitable for rearwheel drive vehicle applications in which the engine is located remotely from the torque output shaft, the torque output shaft being connected to rear vehicle traction wheels through a driveline in known fashion. If an arrangement of this type is configured for a front wheel drive vehicle applications, torque transfer gears in a three axis arrangement must be used to provide a torque flow path from the torque output shaft to the front traction wheels. A configuration of this type would present a problem for packaging the two motor-generators with the torque transfer gearing because the transverse dimension of the powertrain would be unacceptable, especially since the two motor-generators, even in the case of a rear wheel drive configuration, require a large transverse dimension.
The torque transfer gears for the front traction wheels, in a front wheel drive configuration, must be located at the torque output end of the gearing remotely from the engine, which is located at the opposite end of the gearing. It is this feature that results in greater packaging incompatibility for such a two-mode, front wheel drive hybrid vehicle powertrain compared to a conventional powertrain system. It also requires larger transverse dimensions of the vehicle chassis layout.